Do note that Stug-E becoming better, and more consistent vs stationary infantry is the intended design.
The trade-off here, is that stug-E should be considerably worse vs mobile infantry.
Also note that a Stug-E costs about half of the resources that a Brummbar requires. Thus, 2x Stug-E's should be somewhat comparable. Especially now that Stug-E packs inferior AT utility/durability to the Brummbar.
The days of cheesing the Stug-E commander are over.
However, Stug-E should still have -something- to draw people to picking this commander over the other commanders.
The real stress-test here is how Stug-E performs vs AT guns.
the new stug E is basically another brummbar at this point, with minor stats difference.
The vanilla stug E had two issue, it's too cheap (200mp 75 fuel 8 pop is a steal) and the main gun stun is too powerful.
I really have to stress how cheap the vanilla stug E is. At 200 mp 75 fuel it's only 5 fuel more expensive than the vanilla t70. The t70 might be the better infantry killer, but the stug E is just a much better overall package.
I think your solution is over complicating the issue by changing it into a new units.
and the doctrine itself have issue in 2v2+ because of the lackluster Tiger and Assault grenadier.